Trying to think if I have seen something similar before. There were a few games that suffered from "must showcase the DS hardware" that got fixed by hackers but most things had the mic as an optional extra.
Either way it would make for a nice enough control modding hack. The mic is not just another button as far as the hardware is concerned (shutting the screen is another button) but might as well be for the purposes of this sort of hack.
Much like a more conventional higher end control hack you would find the loop that the game does to look for the mic having sound coming from it (few DS games will try to do anything like voice analysis), and it will likely be a time window as well and point it instead at the debounced* controls.
*if you look at something like
http://problemkaputt.de/gbatek.htm#dskeypad it will say where the console puts the state of the buttons in memory. Most devs however are encouraged to copy this section to somewhere else in memory and operate on that for the next frame or so. This is as else you find something like two things happen if A is pressed and as switches are not perfect (when pressed the little plates can be closed, can be open... bounce if you will) the following thing might see it as not pressed and then odd behaviour happens.
You could theoretically come the other way and maybe see if the "levels" themselves can change the buttons they want but I doubt it will be the case here. I don't know if each and every minigame with the blowing mechanic will be treated as a separate instance (sometimes with minigame collections they can be their own little standalone, or near as does not matter, piece of code.
Possible super cowboy method. The game might have a section of normal memory that says the microphone is getting enough volume. Find this and you might be able to set it to blow all the time with a cheat (if memory serves you just blow in these minigames, no timing element or anything., or maybe make a button activator cheat.
